Transcript Forensic Toxicology

Forensic Toxicology
O’Connor
Role of Forensic Toxicology
• Forensic toxicologists detect & identify
drugs & poisons in body fluids, tissues, &
organs in matters that pertain to violations
of criminal laws.
• Ethyl alcohol is the most heavily abused
drug in Western countries.
Ethyl Alcohol
• All evidence shows ethyl alcohol (which is
legal if over 21) is the most heavily abused
drug, causing 40% of all traffic deaths in
the US.
• Nearly 17,500 fatalities/year are alcohol
related & over 2 million injuries requiring
hospital care.
Toxicology
• Detect and isolate drugs in the body to
determine their influence on human
behavior.
• Knowing how the body metabolizes
alcohol is key to understanding its effects.
• Knowledge made development of
instruments to measure presence &
concentration of alcohol.
Metabolism of Alcohol
• Metabolism- body breaks down one
chemical into chemicals that are easier for
it to eliminate.
• Three basic steps:
• 1.Absorption
• 2.distribution
• 3.elimination
Metabolism of Alcohol
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Step 1 Absorption
• Consumed as a colorless liquid in a
mixture
• Appears in blood w/in minutes
• Increases in concentration as it is
absorbed by stomach & sm. intestines into
bloodstream
• Absorption to the blood allows the alcohol
to be carried to all parts of the body
Distribution
• The body is 2/3 water and the alcohol gets distributed
evenly through the bodies liquid parts.
• The timeframe for rate of absorption/distribution:
• Total time taken to consume
• Amount consumed
• Quantity & type of food present in stomach
• Size of individual consuming total volume of liquid
present in the body)
Elimination
• As the alcohol is circulated by bloodstream, the
body begins to eliminate it by two processes,
oxidation & excretion.
• 95-98% is oxidized to CO2 & H2O starting in the liver
• In the presence of enzyme alcohol dehydrogenase
it is converted into acetaldehyde and then to acetic
acid which is broken down throughout the body to
CO2 & H2O
• Remaining 2-5% is excreted unchanged in the
breath, urine & perspiration (in proportion to level in
blood stream)
“Burn-off” rate of alcohol
• Postabsorption varies by individual
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the average (which can vary by 30%):
• .015% w/v (weight per volume) per hour upon
completed absorption
BAC- blood alcohol Concentration
• Best way to determine- remove a portion
of the brain & analyze for alcohol content
• (problematic for the living)
• Blood alcohol levels are the legally
accepted standard for measurement in the
living. (postmortem- brain, cerebrospinal
fluid, or vitreous humor is tested)
Taking Measurements
• Measure concentration in Blood test
• Measure alcohol content in breath
Henry’s Law is applied:
• When a volatile chemical is dissolved in a
liquid & is brought to equilibrium with air, there
is a fixed ratio between the concentration of
the volatile compound in air & its concentration
in the liquid & this ratio is constant for a given
temperature.
• Breathe leaves the mouth at an ave. of 34°C,
the ratio of alcohol in the blood; to alcohol in
the aveolar air is approximately 2,100 to 1.
(1 ml of blood same amt. alcohol as 2,100ml of breath)
Testing for Intoxication
• Hundreds of thousands of motorists tested
annually.
• Breathe testing, quick- convenient &
reliable
• (early in absorption process- breathe test
will show higher levels than blood tests;
but match effects on the brain)
Breathalyzer
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Developed in 1954 by R.F. Borkenstein
modified over years- basic principles still apply.
Breathalyzer replaced chemical free devises:
Infrared & fuel-cell-based devices controlled by
microprocessors.
Process:
Start with field sobriety test
Nothing taken orally for 15 min. prior to test.
Take two test samples minutes apart
Field Sobriety test
• Used to determine an individuals physical
impairment & to justify further testing
• Series of psychophysical tests:
• Horizontal-gaze nystagmus (follow pen light w/
eyes)
• walk & turn
• One-leg stand
Higher BAC:Higher physical impairment
• .10% BAC = eye jerk before eye has moved 45°
• Other drugs can trigger this effect, phencyclidine,
barbituates, & other depressants)
• Walk/turn & one-leg stand are divided attention
tasks. Requiring ability to understand & carry
out more than 2 instructions: this ability is
affected by blood-alcohol levels.
Blood Analysis
• Forensic toxicologists
must devise an
analytical scheme to
detect, isolate, & identify
toxic drug substances
extracted from biological
fluid, tissues, and
organs.
• A screening test gives quick insight into
the likelihood that a specimen contains a
drug substance.
• Positive results arising from a screening
test are tentative at best and must be
verified with a confirmation test.
• The most widely used screening tests are thinlayer chromatography, gas chromatography,
and immunoassay.
• Gas chromotography/mass spectrometry is
generally accepted as the confirmation test of
choice.
• Once a drug is extracted & identified, a
toxicologist may be required to judge the
drug’s effect on an individual’s natural
performance or physical state.
• This is different depending on whether the
individual is a live or deceased.
• Field sobriety results come into play for
the living. (much easier to use in court
since video camera’s were added to police
vehicles)
• Deceased, requires the ME to determine
cause of death, for this the ME and
toxicologist work together.
Alcohol Intoxication vs Drug Induced Intoxication
• Alcohol intoxication is widely recognized, police
are highly trained for & the courts are
accustomed to the effects.
• Drug Induced Intoxication is harder to recognize.
In the 1970s they developed & tested a series of
clinical & psychophysical examinations that a
trained police officer could use. The program is
now used nationwide to train drug recognition
experts (DRE); a 3-5 month training program is
required to certify.